title: Effects of self-assembled monolayer structural order, surface homogeneity and surface energy on pentacene morphology and thin film transistor device performance.
abstract: A systematic study of six phosphonic acid (PA) self-assembled monolayers (SAMs) with tailored molecular structures is performed to evaluate their effectiveness as dielectric modifying layers in organic field-effect transistors (OFETs) and determine the relationship between SAM structural order, surface homogeneity, and surface energy in dictating device performance. SAM structures and surface properties are examined by near edge X-ray absorption fine structure (NEXAFS) spectroscopy, contact angle goniometry, and atomic force microscopy (AFM). Top-contact pentacene OFET devices are fabricated on SAM modified Si with a thermally grown oxide layer as a dielectric. For less ordered methyl- and phenyl-terminated alkyl ~(CH2)12PA SAMs of varying surface energies, pentacene OFETs show high charge carrier mobilities up to 4.1 cm2V-1s-1. It is hypothesized that for these SAMs, mitigation of molecular scale roughness and subsequent control of surface homogeneity allow for large pentacene grain growth leading to high performance pentacene OFET devices. PA SAMs that contain bulky terminal groups or are highly crystalline in nature do not allow for a homogenous surface at a molecular level and result in charge carrier mobilities of 1.3 cm2V-1s-1or less. For all molecules used in this study, no causal relationship between SAM surface energy and charge carrier mobility in pentacene FET devices is observed.
authors.affiliation: Department of Materials Science and Engineering, University of Washington, Box 352120, Seattle, WA 98195-2120, USA.
authors.forename: Daniel Orrin
authors.initials: DO
authors.lastname: Hutchins
authors.forename: Tobias
authors.initials: T
authors.lastname: Weidner
authors.forename: Joe
authors.initials: J
authors.lastname: Baio
authors.forename: Brent
authors.initials: B
authors.lastname: Polishak
authors.forename: Orb
authors.initials: O
authors.lastname: Acton
authors.forename: Nathan
authors.initials: N
authors.lastname: Cernetic
authors.forename: Hong
authors.initials: H
authors.lastname: Ma
authors.forename: Alex K-Y
authors.initials: AK
authors.lastname: Jen